An important factor in cattle breeding is fertility. Fertility manifests itself in sperm count and semen quality. It is a highly heritable trait. Unless the cattle are selected on the basis of their fertility genetic degeneration of the cattle herd is the inevitable result. Determinations of fertility have focused on bulls, for it is difficult to determine the fertility of cows. It has been established, however, that a bull of above average fertility will have female progeny of above average fertility.
It has been determined that there is a correlation in bulls between testicular weight and sperm production. Sperm production is recognized as being a factor in fertility. There is a correlation between scrotal circumference measurement and weight. As it is not practical to weigh the scrotum of a live bull, efforts to determine fertility have focused upon scrotal measurement. Experts have conducted studies to determine a range of scrotal circumference of bulls according to age and breed. From these ranges they have been able to determine average scrotal circumference and set minimum recommended scrotal circumference in order to avoid genetic degeneration relating to fertility. One such study, a cooperative effort between the Agriculture Canada Research Station at Lethbridge, Alberta and the Western College of Veterinary Medicine at the University of Saskatchewan, is documented in an article by G. H. Coulter, R. J. Mapletoft and W. F. Cates entitled "Scrotal Circumference of Two Year Old Bulls of Several Beef Breeds" which appeared in March 1987 issue Volume 27 No. 3 of Theriogenology.
The measurements and their significance is predicated upon measuring the scrotum with a measuring tape while applying "moderate resistance". It is recognized that care must be taken not to cause trauma to the bull's testes as such trauma results in inflammation which has a detrimental effect on the sperm producing capability of the bull. Depending upon the severity of the trauma such inflammation can effect fertility for weeks or months. On the other hand, if insufficient tension is applied the result gives an inaccurate and misleading indication as to fertility. For example, in the above mentioned article the scrotal circumference for yearling Aberdeen Angus bulls varies between 24.5 and 40.0 centimetres with a mean of 33.9. Bulls with a scrotal circumference below 32 centimetres were not recommended as breeding bulls. An error in measurement of one or more centimetres can have dramatic effects on a breeding program.
Major sales of cattle breeding stock are implementing minimum scrotal measurements as a prerequisite for accepting bulls. It has been discovered, however, that there are only a very few experts in the field who can perform consistent and repeatable manual scrotal circumference measurements. Farmers are relying upon inaccurate scrotal measurements when entering cattle sales. Often they pay entry fees and travel great distances to such sales only to discover that their bulls do not meet the minimum scrotal measurement requirements.
Apparatus exist for performing diverse types of circumferential measurement. The most closely analogous apparatus is U.S. Pat. No. 2,129,582 which issued to Johansson in 1938. This Patent discloses a spring biased tape forming a loop. This type of apparatus is not usable for scrotal measurement without modifications for a number of reasons. On fundamental reason is that the spring tension used in such measuring devices does not approach the "moderate resistance" recommended for scrotal circumference measurement. It is a matter of a great deal of experimentation and study to determine what tension can be equated to "moderate resistance" applied manually by a cattle expert.